Increased regulation of emissions from gas turbine engines has prompted the development of thermally efficient and reduced emission fuel injectors. It is known that carbon monoxide (CO) and unburned hydrocarbons (UHC) emissions can be reduced with high temperature combustion in the engine. However, high temperature combustion can result in increased production of nitrogen oxides (NOX). This problem has been addressed by injectors which are configured more thoroughly to mix fuel with air prior to combustion with a fuel-to-air ratio below the stoichiometric level. Such arrangements can provide a “lean burn” which results in lower flame temperatures than would occur with stoichiometric burning. Since the production of NOX is a strong function of temperature, a reduced flame temperature or “lean burn” results in lower levels of NOX.
Staged fuel injection is known to result in reduced engine emissions. In such arrangements, the combustion process is divided into two (or more) zones or stages. These stages are typically physically separate from each other, but close enough to permit interaction. Separation can be axial and/or radial separation. A first, pilot stage is configured to provide fuel for low power operations. In higher power conditions, the pilot continues to provide fuel to the engine and in addition a second, main stage provides the remaining fuel needed for engine operation. In this way, proper fuel-to-air ratios can be controlled for efficient combustion, reduced emissions, and good stability.
Along with staged combustion, pollutant emissions can be reduced by providing a more thoroughly mixed fuel-air mixture prior to combustion wherein the fuel-to-air ratio is below the stoichiometric level so that the combustion occurs at lean conditions. Lean burning results in lower flame temperatures than would occur with stoichiometric burning. Since the production of NOX is a strong function of temperature, a reduced flame temperature results in lower levels of NOX. The technology of directly injecting liquid fuel into the combustion chamber and enabling rapid mixing with air at lean fuel-to-air ratios is called lean direct injection (LDI).
Components of the nozzle which sit furthest into the combustion chamber are exposed to extreme mechanical and thermal loading and are consequently provided from high performance alloys. The combustion chamber is sealed around the fuel injector to prevent leakage of combustor product upstream of the gas turbine engine.
Additive layer manufacturing (ALM) methods are known. In these methods a component is built up layer by layer until the 3D component is defined. In some ALM methods, layers are created by selective treatment of layers within a mass of particulate material, the treatment causing cohesion of selected regions of particulates into a solid mass. For example, the particulate is a ferrous or non-ferrous alloy powder and the treatment involves local heating using a laser or electron beam. Specific examples of such ALM methods include (without limitation); laser sintering, laser melting and electron beam melting (EBM).
Laser consolidation is a known method of manufacturing, repairing or restoring blades of gas turbine engines. The process involves creating a melt pool at a metal surface using a laser. A metal or ceramic powder is delivered by a nozzle into the melt pool and three-dimensional geometry is built up. U.S. Pat. Nos. 6,269,540 and 7,984,547 describe examples of this process. U.S. Patent Application Publication No. 2013/0298403 describes the use of such a process to strengthen components of a fuel injector by adding local patches of a second (mechanically stronger) material to areas of weakness identified on a main body of the component. The specific description therein is particularly directed to outer surfaces of the feed arm.
There is a desire to increase the operational life of staged fuel injectors.